Control system



H. KEI' I'H I common SYSTEM 7 Filed May 23, 1919 WITNESSES: INVENTOR [WW ATTORN EY Patented Sept. 13, 1927. i

UNITED STATES PATENT OFFICE.

HAROLD L. KEITH, 0F WILKINSBURG, PENN SYLVANIA', ASSIGNOR T0 WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

CONTROL SYSTEM.

Application filed ma 23,

maintain the relays open for a predetermined length of time, or so long as the current is above a predetermined value, after every operation of short-circuiting a-portion of the accelerating resistor. As the motor current rises from a comparatively low to a comparatively high value after every short circuiting operation, these systems are sub-' ject to the disadvantage that the relays may close prematurely, before the motor current can build up to values sufficiently large to hold them open. To make these systems practical, it is necessary to mechanically interlock the contactors and the relays and to provide additionalmeans for maintaining the relays open until the current builds up to the required holding values.

In a co-pending application by H. D. James. Serial No. 236,937, filed May 27, 1918, which has matured into Patent No. 1,392,056 and is assigned to the Westinghouse Electric'& Manufacturing Co, the mechanical interlock andthe additional maintaining means are avoided by subjecting therelay coils to a uniformly decreasing voltage instead of to the variable conditions resulting from the successivemotor-current peaks.

An object of myinvention is to provide an accelerating system of the above-designated character, the relays of which shall be adapted to operate at substantially constant voltage.

Another object is to provide such a system which shall be adapted to control also the speed of the motor.

A further object is to provide a novel accelerating system with'the use of which it shall be impossible to reverse the motor until after'the accelerating resistor has first been reinserted into the motor circuit.

Other objects of my invention will a 7 pear in connection with the, following escription.

The coil of the first relay to operate is normally energized by line voltage to a degree' great enough to maintain the relay 1919. Serial No. 299,181. open. Upon the closing of the motor circuit, the coil becomes connected across a small port-ion of the accelerating resistor. As the motor accelerates, and the voltage of this resistor portion decreases, in consequence, the relay becomes closed by gravity, effecting the actuation ofthe first resistorshort circuiting contactor. The coil of the second relay to operate is connected between a point of the now short-circuited section of the resistor and a point of the next section" to be short-circuited. The ohmic value of the portion of the resistor that is'between' these points is so great as to c ause the relay to be maintained open. When, however, the first section of the resistor becomes shortcircuited, the ohmic value of the remaining portion which is then effective to control the relay coil becomes much reduced so that the second relay, may ultimately be closed, in the same manner as the first relay, in accordance with the current conditions of the mo-.

tor. The remaining relaycoils are similarly connected between points of two successive resistor sections and are adapted to be closed by gravity in similar fashion. It is thus impossible for the relays to close prematurely and they may be designed to close at the same voltage or at any desired voltages. My system is advantageous for use in connection with speed control. I provide a resistor that is adapted to be connected in parallel relation to the motor armature to effect a slowing down of the motor, whereupon the relays may again open and, upon disconnecting the parallel-connected resistor, the motor. may again be accelerated as'before.

In the accompanying drawings, Figure 1 is a diagrammatic View of circuits and appa-- ratus embodying. my invention. Fig. 2 is a similar view of a modification.

Line conductors 1 and 2, which may be connected to any suitable source of direct and 21, that are under the control of relays 22, 23 and 24, and switches 25 and 26 that are i mechanically connected to the reversing contactors 7 and 8. The switches 25 and 26' are open when the contactors 7. and 8 are open and are closed when these contactors are closed.' A pair of switches 27 and 28 are also respectively mechanically connected to the reversin contactors 7 and 8 for respect1vely contro ling the circuits of the coils 10 and 12, and 11 and 13. Switches 125 and 126 'are'mechanically connected to the contactors 9 and 6 so as to open and close with the corresponding contactors.

The relay 22'is provided with an energizing coil 29 that 'is connected in series with a resistor 30 ofhigh ohmic value between the line'conductors 1 and 2. The coil 29 is also connected, in circuit with the switch 125 or the switch "126, across the.

'unction points 31 and 32 of the resistor 15.

he rela 23 is provided with an energizingcoil 33 t at is connected, in circuit with the switch 125 or the switch 126, between junction points 32 and 34 of the resistor 15..

that is adapted to be opened by a coil 72.

through a contact member 60 in the second position of the master switch 14.

, The operation is as follows: upon the actuation of the master switch 14, to the right or to the left, the reversing switch coils 10 and 12 or 11 and 13 will become energized to effect the operation of the motor in the one or the other direction. Assumin that the master switch is actuated to the fight, to its first osition, a circuit is established from the line conductor 1, through the coil 12, the switch 27.which is closed when the contactor 7 is openthe coil 10 and the master switch'14, to the line conductor 2. The contactors 8 and 6 become closed thereupon to establish the motor circuit, which extends from the line conductor 1, through the contactor 8, the armature 4, the contactor 6 and the resistor 15, to the line conductor'2. The shunt field-magnet windin 5 and the coil 29 are normally continual y energized when the line conductors 1 and 2 are energized, the circuit of thecoil 29 extending romthe line conductor 1, through the resistor 30 and the coil 29,to the line conductor 2. When the resistor 15 becomes-ene ized, upon the closing of the motor circu t, however, the coil- 29 becomes energized by1t-he -potentia1 drop -between the points 31' taintherelay 23 open.

and 32, its circuit extending from the 'unction point 31, through the coil 29, y a conductor'41, and through the switch 126, to the junction point.32. v As the motor continues to accelerate, the potential drop just mentioned becomes smaller until, after a time, the coil 29 will be energized by a voltage which is insuflicient to maintain the relay 22 open. The relay 22 will thereupon become closed by gravity.

A circuit will be thereupon established for the coil-19, assuming that the master switch 14 has been actuated to its second position, from the line conductor 1, through the reversing contactor 8, the switch 26, the relay 22, the coils 19 and 72 and the contact member 60 of the master switch 14, to the line conductor 2. Energizat-ion of the coil whereupon the portion of the resistor 15 between the junction points'31 and 36 becomes short-circuited.

Simultaneously with the energization of the coil 29 by the resistor portion between the junction points 31 and 32, the coil 33 will become energized by the resistor portion between the junction points 32 and 34, and the coil 35 will become energized by the resistor portion between the junction points 36 and 37. These resistor portions and the relay coils 33 and 35 are so designed that, when the coils 33 and 35 are respectively connected between the points 32 and 34 and the points 36 and 37, the voltage drop is so great as to maintain the relays 23 and 24 open, irrespective of the accelerating condition of the motor. Upon the closing of 19 effects the closing'of the contactor 16,

the contactor 16, however, to efi'ect the shortcircuiting of the resistor portion between the jllIlCiSlOIl points 31 and 36, the relay coil 33 is no longer subjected to the potential difference between the junction points 32 and 34 because the resistor portion between the points 32 and 36, being short-circuited, is no longer energized by the motor current. The relay coil 33, therefore, becomes subjected to the voltage differential between the junction-points 36 and 34. After the motor has accelerated sufliciently, the voltage drop across the resistor portion between the junction points 36 and 34 becomes small enough so that the coil 33 is no longer able to main- I The relay 23 becomes thereupon closed by gravity. The relay 24, however, remains still open.

Upon the closing of the relay 23, a circuit is established from the line conductor 1, throu h the'contactor 8, the switch 26, relay 22, re ay 23 and the coil 20 to the line conductor 2, efiecting the energization of the coil 20 and the consequent closingof the contactor 17. The closing ofthe contactor 17 effects the short-circuiting of the portion of. the resistor 15 between the junction points 36 and g8. The coil 35 becomes thereupon responsive to the voltage drop of the resistor portion between thejunction points 38 and.

lished from the line conductor 1, through the reversing contactor 8, the switch 26, relay 22, relay 24 and the coil .21, to the line conductor 2. The portionof the resistor between junction points 37 and 38 becomes thereby short-circuited and, as the remainder of the resistor has been previously short-'cir cuited, the armature 4 becomes thus connected directly to the line conductors 1 and 2.

It will be noted that, according to my invention, no mechanical interlocks between the short-circuiting contactors 16, 17 and 18 and the relays 22, 23 and 24 are necessary.

.There is not the slightest danger, such as is to be found in present systems involving the use of relays having coils in series with the motor armature, of the relays closin prematurely before the motor current bui ds up to values sufiiciently large to maintain them open. This danger is obviated because the relay coils are normally connected across portions of the resistor such that, so long as those portions are energized by the motor current, the relays will be maintained open. Not until parts of those portions have been short-circuited so as to subject the .relay coils to the potential drop across the remainder of those portions is it possible for the relays to close. Some means, of course, must be provided for maintaining the first relay to operate normally open. I provide this means by energizing the coil 29 from the line conductors 1 and 2 throughthe res1stor 30.

When it is desired to reverse the motor, the master switch 14 will be actuated to the left. The circuits of the actuating coils 10 and 12 of the reversing contactors 6 and 8 will thereupon become de-energized. The

.contactors 6 and .8 will thereupon become opened and the switch 26 will also become opened to effect the openingof the circuits of the coils 19, 20 and 21 The short-circuit ing contactors 16,17 and 18 will thereupon fall open to reinsert the resistor l'iinto the motor circuit. Before the motor 3, therefore, may be started again, either in the same or in the opposite direction, the resistor 15 will be in the armature circuit to prevent subjecting the armature windings to an unduly high voltage.

Upon the master switch 14 being actuated to the left, to its first position, a circuit will be established from the line conductor 1,

throu hthe coil 13, the switch 28. the coil 11 an the master switch 14, to the line conductor 2. If it should happen, therefore, I

that the contactor 8 did ,not open for some reason, upon the circuit of the coil 12 becoming broken by the master switch 14, it will be impossible to establish this circuit for the coils 13 and 11. It will, therefore, not be possible to energize these coils, and operation of the motor in the opposite direction will thereby be prevented.

It is, therefore, impossible to reverse the motor until the switch 26 has become opened to efl'ect the reinsertion into the motor circuit of the resistor 15 and until the switch 28 has closed to effect the closing of the circuit of the coils 13 and 11. In similar fashion, assuming that the motor has been operating in the reverse direction, and that it is desired to operate the motor in the forward direction by again actuating the master switch 14 to the right, it will be impossible to establish the circuit of the actuating coils 12 and 10-this circuit being open at the switch .27-until the contactor 7 has opened the switch 25 to effect the opening of. the circuits of the actuating coils 19, 20 and 21 of the short-circuiting contactors 16, 17 and 18.

Assuming, then, that the reversing contactor 8 has become opened to effect the opening of the switch 26 and the closing of the switch 28, the coils 13 and 11 will become energized by the above-traced circuit to effect the closing of the reversingcontactors 9 and 7 The circuit of the motor is then established for operation in the opposite, direction from the line conductor 1, through the contactor 7, the armature 4, the contactor -9 and the resistor 15, to the line conductor same as above described. The relays 23 and 24 will operate, in similar fashion, to effect the closing of the resistor-short-circuiting contactors 17 and 18, thereby to remove portions of the resistor 15 from the armature circuit and, ultimately, to connect the arma ture 4 directly to the line conductors 1 and 2.

It will be remembered that the circuit of the coil 19 com rises the coil 72 so that, when to effect the opening of the relay 1, thereby breaking the shunt circuit comprising the resistor 70. The above operations have accordingly been described as though there were no resistor 70 in shunt to the armature 4. y

sition inwhich it effects the closing of the When it is desired to vary the speed of the motor, however, (assuming that it is operating under light loads) the master switch 14 may be returned to its first position in which the circuit of the .coils 19 and 72 is broken at the contact member 60. The contactor 16 thereupon falls open by gravity and the relay 71 becomes released, the cont actor effecting the reinsertion into the armature circuit of the resistor portion between the junction points 31 and 36, and the re lay establishing the circuit comprising the resistor 70 in shunt to the armature 4.

The voltage of the resistor 15 becomes, of course, increased in consequence and the relay 22 becomes opened by its actuating coil 29 which is again subjected to the voltage drop between the junction points 31 and 32. Under these conditions, if the master switch 14 should again be actuated to its second pocontact member 60, the. coils 19 and 72 will not immediately become energized, their ci'rcuit being controlled by the relay 22 which i will be maintained open by its energizing applied to an alternating-current motor havcoil 29 so long as the voltage of the resistor 15 is above a predetermined value. The ac-' celeration of the motor will again be controlled, therefore, in accordance with the voltage conditions of the resistor 15.

Ordinarily, the resistor is employed in the case of unidirectional motors only. Obviously, the same result as that .above described may, however, be obtained without the useof the resistor 70 if the motor is operating at a heavy load. For, under such conditions, the yalue of the voltage of the resistor 15 changes more rapidly than is the case when the motor is operating under light loads. Furthermore, it will readily be apparent that-the coils 19, 20 and 21 may be controlled in separate positions of the master switch 14 so that the above-described opera tion of the relay 22 following the establishment of the shunt circuit comprising the resistor 70 may take place in connection with the relays 23 and 24 as well.

In Fig. 2, Ihave shown my invention as ing-a primary winding 5, that isconnected,

by a line contactor 76, to any suitable source of alternating current by line conductors 77, 7 8" and 79, and a's'econdary winding having in circuit therewith a resistor 81 that. is adapted to be short-circuited by a pair of. contactors 82 and 83.hav ing coils 84 and 85,

'nected across the junction points 89 and 92. The ohmic value of the resistor portion between the junction points 88 and 89 is equal to that between the junction points 93 and 92. A slow-acting relay 94, having an ac tuating coil 95 that is connected across the line conductors 77 and 78, is provided to insure the opening of the relay 86 prior to the closing of the slow-acting relay 94 andlthe consequent energization of the coil 84 before the relay 87 becomes energized to eilect the opening of the relay 86 upon the closing of the line contactor 76.

Upon the closing of a master switch to ergized in accordance with the voltage drop I of the resistor portions across which they are connected, so that the relays 86 and 90 become opened. The slow-acting relay 94 becomes later closed by its energizing coil '95 so that, when the relay 86 becomes closed by gravity, following a sufiicient drop in potential between the points 89 and 88, the circuit of the coil 84 becomes established to effect the short-circuiting of the first section of the resistor. So long as the coil 91 is energized in accordance with the potential difference between the points 89 and 92, it cannot become closed. Upon the closing of the contactor 82, however, the coil 91 becpmes subjected to the potential difierence between the points 92 and 93 so that, when the motor speed attains .a sufiiciently high value and t e voltage drop between the polnts 92 and 93 decreases to a sufficiently ow value, the relay 90 will become closed by gravity to establish the circuit of the 0011 85 and the short-circuiting of the re-v maining portion of the resistor 81.

Although I have shown two forms which my lnvention may take, it is obvious that the invention is not restricted to either form but is of much broader scope. I desire, therefore, that the invention be construed broadly except in so far as limitations may be specifically imposed in the appended claims.

I claim as my invention:

1. The combination with an electric motor having'a resistor associated therewith, a plurality of switches for respectively controlling sections of said resistor and a relay for each'of said switches, said relays having actuating coils the terminals of-which are 60 respectively. The circuit of the coil 841% connected tov intermediate points of adjacontrolled by a relay 86 having an energizing coil 87 that is connected across the junction oints 88a'nd 89 oi, the resistor, and the circuit of the coil 85 is controlled. by a relay 90 having an actuatingcoil91 that is concent sections, of means whereby said relays restrain the corresponding switches until the voltage of said coilssuccessively decreases to substantially the same value. 2. The combination with an electric motor having a resistor associated therewith, of a plurality of switches for respectively short circuiting sections of said resistor, and a plurality 'ofl relays for governing, 'said switches and having energizing coils respectively connected across portions of pairs of adjacent sections of said resistor.

3. The combination with an electric motor having an armature, a resistor in series therewith, a plurality of switches for respectively short-circuitin sections of said resistor and a relay or each, of said switches, of an ener izing coil for each of said relays respective y connected across portions of adjacent sections of said resistor the pairs of adjacent portions having equal ohmic values.

4. The combination with an electric motor having a resistor associated therewith, and a Y switch for controlling said -resistor having an energizing coil, of means for normally maintaining said coil energized to maintain said switch open and means for connecting said coil. across saidresistor upon the closing of the circuit of said motor. I

The combination with an'electric motor he ring an armature, a resistor in series therew .h. source of energy for said motor, apiu. Jity of switches for short-circuitin said resistor and a relay for each of sai switches, said relays having ener izing coils controlled in accordance with t e voltage drop of-said resistor, of means for maintaining the coil of the first of said relays to operate'energized from said source when said motor is disconnected from said source.

6. The combination with an electric motor havin a resistor associated therewith, and a plum ity of switches for successively con-' trolling portions of said resistor, of a relay for each of said switches having an energizing coil connected to points in each of two of saidportions of said resistor.

7. In combination, an electric motor having an armature, a resistor inseries therewith, a pair of switches for successively short-circuiting two sections of said resistor, and arch for each of said switches, the first of sai relays to operate having an energizing coil connected across a portion, of the first of said two sections of said resistor ,to'be short circuited, and the second of said relays to operate having an energizin coil connected across a portion of botho said.

two sections of said resistor, whereby said first relay may he closed in accordance with the current-conditions of said motor and said second relay meme closed only after the closing of said relay.

8. The motor havin an armature, and a resistor in series therewith, a switch for short-circuitin said resistor having an actuating coil an a switch for closing the circuit or said motor, of a relay for controlling the circuit connected across a portion of said resistor,

combinationwith an electric ,of said coil and having an energizing coil and a switch mechanically connected to said circuit-closin switch and in circuit with said relay ang said coil. I

9. The combination with an electric motor and a resistor associated therewith, of

cessive short-.circuiting of various sections of said resistor, said switches having actuating coils influenced 1n accordance with the voltage between certain intermediate points of of a plurality of switches biased to elfect .a plurality of switches for efiecting the suc- V the short-circuiting of portions of said resistor, .said switches having actuating coils energized in accordance with the voltages of parts of a plurality of selected portions of said resistor for opposing said biased effect uponsaid switches. I 12. The v motor and a resistor associated therewith, of a plurality of switches for controlling ortions of said resistor, said'switches having actuating coilsenergized responsively to the voltages of parts of a plurality of selected portions of said resistor. Y

13. A control system comprisin a resistor, aplurality ,of switches for s ort-circuiting sections thereof, rela devices for controlling saidswitches, sai relay device coils being initially connected across portions of the resistor sufiicient to maintain the relay devices open, the relay devices being rendered operative by the sucessive closure of said switches to connect said coils across equal active portions of said resiston.

In testimony whereof, I have hereunto subscribed my name this 16th day of May,

. HAROLD L. KEITH.

cornb'nation with an electric 

